A typical multi-optical axis photoelectric sensor includes an emitter unit, which includes a plurality of emitter elements aligned linearly, and a receiver unit, which includes a plurality of receiver elements aligned linearly in one-to-one correspondence to the emitter elements. The emitter elements and the receiver elements are arranged to face each other in one-to-one correspondence and define a detection area formed by a plurality of optical axes.
The emitter unit sequentially lights their emitter elements. The receiver unit determines the amount of light received by each of the receiver elements in synchronization with the lighting operation of the emitter elements. The emitter unit sequentially detects the interrupted state of each of the optical axes of the multi-optical axis photoelectric sensor. The receiver unit determines whether an object is in the detection area based on the detection result for each optical axis, and outputs a signal indicating the determination result. The emitter unit and the receiver unit are connected with a communication line to allow synchronization between the emitter and receiver units. The emitter unit and the receiver unit may be synchronized with each other by optical communication between them.
The multi-optical axis photoelectric sensor is installed, for example, on a production site to achieve the safety of workers. For example, when detecting an interrupted state of any of the optical axes in the detection area, the multi-optical axis photoelectric sensor stops the operation of the manufacturing equipment. However, the manufacturing system may be used in an environment in which some of the optical axes in the detection area of the multi-optical axis photoelectric sensor are constantly interrupted by a specific object, such as a workpiece. For such an application, the multi-optical axis photoelectric sensor has blanking, which can nullify the optical axes that are interrupted by a specific object. Such blanking may either be fixed blanking, which is used for a light interrupting object that is stationary within the detection area, or floating blanking, which is used for a light interrupting object that is movable within the detection area.
As described above, the multi-optical axis photoelectric sensor provides safety function by immediately stopping the operation of the manufacturing equipment upon detecting any optical axis interrupted in the detection area, independently of the number of interrupted optical axes. In contrast, the sensor with blanking stops the operation of the manufacturing equipment upon detecting that any of the optical axes excluding the optical axes satisfying predetermined conditions is interrupted in the detection area. The optical axes satisfying the predetermined conditions can be set freely by the user in accordance with the size and the position of the light interrupting object in the detection area. More specifically, the sensor with fixed blanking allows the user to select optical axes to be nullified in the detection area. The sensor with floating blanking allows the user to determine the number of optical axes to be nullified.
For example, Japanese Unexamined Patent Application Publication No. 2-271199 (Patent Literature 1) describes a photoelectric safety device for a machine tool. This safety device scans all the optical axes in a setup mode and stores optical axes for which light interruption has been detected. When detecting light interruption of any of the optical axes excluding the optical axes that have been stored in subsequent scanning performed in an operational mode, the safety device determines that an object other than a preset light interrupting object has entered a dangerous area, and outputs a stop signal to the machine tool.
Another multi-optical axis safety device with floating blanking described in Japanese Patent No. 4481549 (Patent Literature 2) sets a floating blanking area as a part of the detection area. This safety device implements floating blanking in the floating blanking area and implements normal safety function in the other area. The safety device described in Patent Literature 2 sets the floating blanking area through teaching. More specifically, a light interrupting object is placed in an area to be set as the floating blanking area. While the object is interrupting light, the teaching button is pushed to set the floating blanking area. This sets the other area without the light interrupting object as an area in which normal operation is to be performed.